Effective Methods for Blowing a Pull String Through Conduit

[MikePhua]

Blowing a pull string through conduit is a standard practice in electrical and telecommunications installations. It’s a relatively simple task but requires the right techniques and tools to ensure efficiency and prevent damage to the conduit or cable. Whether you are installing new wiring, fiber optics, or other cables through underground or overhead conduits, understanding how to properly blow a pull string is critical for successful installations.
What Is a Pull String and Why Is It Important?
A pull string is a strong, thin rope or cord used to pull electrical or communication cables through conduits. It’s often used when the conduit is long, tight, or filled with obstacles that would make it difficult to manually pull the cable. The pull string helps guide the cable through the conduit and is an essential tool for professionals in the construction, telecommunications, and electrical fields.
In many cases, pull strings are used to guide a heavier and bulkier cable into the conduit after the string has been fed through. This is especially important when dealing with larger conduits or long distances. The string can be attached to the cable, and by pulling the string, the cable is drawn into place without having to physically push or drag it through the conduit.
Steps for Blowing a Pull String Through Conduit
Blowing a pull string involves the use of a specialized device called a conduit blower or pneumatic air jet. This equipment uses compressed air to push the pull string through the conduit. Below are the key steps for efficiently completing this task:

1. Prepare the Conduit and Work Area: Before starting, ensure that the conduit is clear of any debris, sharp edges, or previous cables that could hinder the passage of the pull string. If you are working with an existing conduit, check for any obstructions that may block the airflow.
   
2. Set Up the Blower Equipment: A conduit blower is typically a high-pressure air device connected to the conduit. Set up the blower by attaching the hose to the inlet of the conduit. Ensure that the equipment is properly secured and that all connections are airtight to prevent any air leakage.
   
3. Insert the Pull String into the Conduit: With the air blower in place, insert one end of the pull string into the conduit. It’s essential to secure the string properly so that it stays in place and doesn’t get blown out of the conduit during the process.
   
4. Use Air Pressure to Push the String Through: Activate the air blower to begin blowing air through the conduit. The air should move the pull string forward through the conduit. If the conduit is long or the airflow seems weak, you may need to increase the air pressure or take breaks to allow the air to build up.
   
5. Monitor the Progress: It’s important to keep an eye on the process to ensure that the string is moving smoothly. If you encounter resistance, it may indicate that there’s a bend or obstruction in the conduit. In such cases, adjusting the air pressure or trying a different method may be required.
   
6. Pull the String Through: Once the pull string has reached the desired end of the conduit, you can either remove the air blower or cut off the excess string. The pull string is now ready to be used to guide cables or wires through the conduit.
   

Common Challenges and How to Overcome Them
Blowing a pull string through conduit might seem straightforward, but several challenges can arise. Understanding these issues and how to handle them is essential for successful installations:

1. Clogs and Obstructions: Sometimes, debris or previous cables may clog the conduit. This can create resistance, making it difficult to blow the pull string through. In this case, use a conduit sweeper or a vacuum to clear out any blockages before attempting the blow again.
   
2. Bends and Tight Corners: Long stretches of conduit may have sharp bends, which can prevent the pull string from passing through smoothly. To navigate these, it’s important to apply steady pressure and, if necessary, use a lubricant designed for conduit use to help the string slide through.
   
3. Insufficient Air Pressure: A lack of air pressure is one of the most common reasons for failure during the blowing process. If the string is not moving, ensure that the air compressor is adequately sized for the task and that all connections are tight to prevent leaks.
   
4. String Breakage: If the pull string breaks during the process, it’s often due to excessive pressure or the string getting caught on an obstruction. Using a stronger string or reducing the air pressure may help prevent breakage.
   

Choosing the Right Equipment for the Job
The right equipment is key to successfully blowing a pull string through conduit. When selecting tools and materials for the task, consider the following:

1. Conduit Blower: The blower should be capable of generating enough air pressure to move the pull string through the entire length of the conduit. Pneumatic blowers are typically used for longer distances, while smaller electric blowers may be sufficient for short runs. Make sure to check the specifications of the blower to ensure it matches the size and length of the conduit you're working with.
   
2. Pull String: The pull string needs to be durable enough to withstand the pressure of being blown through the conduit without snapping. Typically, braided nylon or polyester strings are ideal, as they offer strength and flexibility. The string should be slightly longer than the length of the conduit to allow for easy handling on both ends.
   
3. Air Compressor: An appropriately sized air compressor is essential for generating the necessary pressure. A larger compressor may be needed for longer or more difficult runs. Be sure to check that the compressor’s output pressure and volume meet the requirements of the blower.
   
4. Conduit Lubricant: For particularly tight runs or complex conduit systems with multiple bends, lubricant can help the string move more easily. There are specific lubricants designed for use in electrical installations that won't degrade the string or clog the conduit.
   

Best Practices for Efficient Pull String Installation
While the process of blowing a pull string can be straightforward, following these best practices can enhance the efficiency and reliability of the operation:

1. Pre-Check the Conduit: Before inserting the pull string, inspect the conduit to ensure that it’s free of sharp edges, debris, and any other issues that could impede the string’s movement. If the conduit is long and has bends, consider using a conduit inspection camera to check for any hidden problems.
   
2. Work in Sections: For long conduit runs, it can be helpful to break the work into manageable sections. Start by blowing the string through shorter lengths of conduit, then connect them together as you go.
   
3. Secure the String Properly: Ensure that the pull string is securely tied to the cables you plan to pull through the conduit. A common method is to use a figure-eight knot or a loop, which will prevent the string from slipping off when you begin the actual pulling process.
   
4. Use Proper Safety Gear: When working with compressed air and heavy equipment, safety should always be a priority. Wear appropriate safety gear such as goggles, gloves, and hearing protection to prevent injury during the installation process.
   

Conclusion
Blowing a pull string through conduit is an essential skill for anyone involved in electrical or telecommunications installations. By understanding the correct procedures and best practices, as well as using the right tools and equipment, you can ensure the job is completed efficiently and safely. With proper maintenance, this technique can save time and effort, ultimately helping to streamline the process of wiring installations for projects of all sizes.